Occupational Audiometric Testing Part 2: Interpretation and Referral

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1 Occupational Audiometric Testing Part 2: Interpretation and ReferralThomas W. Rimmer, ScD, CIHFay W. Boozman College of Public HealthUniversity of Arkansas for Medical SciencesThis is the second part of the lecture on occupational audiometric testing. In this part we’ll look at how to interpret audiograms according to the OSHA regulations and what actions to take after doing the interpretation. Also covered will be interpretation of audiograms to determine degree of impairment (for workers’ compensation purposes) and also when the audiometric technician needs to refer a subject for professional testing by an audiologist.This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivs 2.5 License. To view a copy of this license, visit

2 Interpretation of resultsComparison of annual to baseline, one ear at a timeThresholdAnnual – ThresholdBaseline = threshold shift50010002000300040006000Baseline, RE201525Annual, RE3540Threshold shift510The most basic element in the interpretation of the results is comparison of the annual audiogram to the baseline audiogram. We do this for each ear separately, so we’re doing this comparison for the right ear on the annual test compared to the right ear on the baseline and then for the left ear on the annual compared to the left ear on the baseline. If we subtract the threshold on the baseline audiogram at each frequency from the threshold at that same frequency on the annual audiogram, that gives us what is called the “threshold shift”. In the chart on this slide, you see the baseline and annual thresholds for the right ear. Subtracting the baseline from the annual results gives us the threshold shift for our example, which ranges from 0 dB to 15 dB. Once we have this information, then we can do further interpretation.

3 Standard Threshold Shift (STS)≥10 dB average shift at 2, 3 & 4 kHzEach ear computed separately≥10 dB average shift in either ear is STSEither average shifts or subtract threshold averages200030004000AVGBaseline, RE152025Annual, RE3531.7Threshold shift1011.7Once we have the threshold shifts computed, we will look more specifically at the results at 2000, 3000, and 4000 Hertz to see if what’s known as a “standard threshold shift” has occurred. The STS is defined as greater than or equal to a 10 dB average shift at those three frequencies, which are the frequencies that are most sensitive to the effects of noise. The idea is that if at least 10 dB of hearing loss has occurred, then we need to be looking at the person more closely to see if we can stop the hearing loss before it progresses. By using three frequencies, we avoid over-identifying STSs, because presumably random errors will average out over the three frequencies. To compute the STS, each ear is calculated separately and if we find the 10 dB or greater shift in either ear, then an STS has been identified, at least on an interim basis, until it can be confirmed. Computationally, you can either average the three threshold shifts, or you can subtract the average of the thresholds at the three frequencies. If you look at the table on this slide, you can see that we are looking at one ear, and if we were to take the average at 2, 3, and 4000 for the baseline, the thresholds would average 20 dB. On the annual audiogram, the average threshold at those 3 frequencies would be 31.7 dB. The difference in those two average thresholds is 11.7 dB. Doing it the other way, we find the threshold shifts at 2, 3, and 4000, which are 10, 15 and 10 dB, respectively. Adding those and dividing by three also gives us an average of 11.7 dB. Either way you do it, gives you the same result. In this case, the result of 11.7 dB is greater than 10 dB, so we have tentatively identified an STS for this particular individual.

4 Other factors in STS determinationTest error or short term lossRetest allowed within 30 daysAge correction allowedSubtracts normal aging loss from threshold shiftAge30405060M2.36.011.719.0F2.04.37.7There are other factors in STS determination, beyond the mere computation of average threshold shift. One of these is an allowance for the possibility of errors in the test or the presence of short-term hearing loss, which would make the computation invalid. The STS is supposed to be a reflection of a person’s permanent hearing status, not of a temporary condition. Therefore OSHA regulations allow for the use of a re-test within 30 days after the initial determination of the STS. The re-test is optional, but most employers will take advantage of this opportunity to confirm or rule out the presence of a true STS.Another factor is that age correction is allowed. The STS is intended to reflect an abnormal hearing loss. The normal or expected hearing loss due to aging is therefore allowed to be subtracted from the threshold shift to determine the amount of hearing loss above and beyond what is due to aging. The normal age-related loss used in the calculation is provided in an appendix to the OSHA hearing conservation regulations, and the table on this slide is provided to give a small example of what this information looks like. This table shows the amount of hearing loss compared to hearing at age 20, for males and females separately, because men tend to have more hearing loss than women as they age. So for example, if the baseline audiogram was at age 20 and the annual audiogram at which we are now looking was at age 30, the average man would have lost 2.3 dB of hearing at the 2, 3 and 4000 Hz frequencies. That value, 2.3 dB, should be subtracted from the computed threshold shift to see if the age-corrected shift still equals or exceeds 10 dB. As one gets further and further from age 20, of course, the amount of “normal” hearing loss continues to grow. By age 60, the average loss for men at the critical frequencies has now reached 19 dB compared to age 20, almost twice the amount required to identify an STS, but we really wouldn’t want to label that as an STS situation, since the STS should be reserved for “abnormal” hearing loss. Age correction will take care of that potential. Of course, in most situations we aren’t comparing to age 20. For example, if the baseline is at age 27 and the annual at age 33, you would have to look at the tables in the OSHA regulation, and the amount of age correction over that 6 year period would be quite small.

5 STS - work related? Determination by health care professionalFactors for determinationWorkplace noise exposureHearing protection on the jobNon-occupational factorsNoisy hobbies, sports, other jobsLack of protectionOnly make determination of non-work-related if no significant contribution to hearing loss due to workplace factorsThe third factor in making a determination of an STS is work-relatedness. No matter what the computed average threshold shift may be, after correction for aging and a possible re-test, the hearing loss must be determined to be work-related to be recorded and dealt with as an STS. That determination has to be made by a health-care professional, preferably the person supervising the audiometric test program. This determination should be based on the person’s noise exposure, the extent to which they are protected from the exposure, and off-the-job factors. Let’s take a simple example: a person is exposed to a time weighted average of 85 dBA, wears earmuffs at all times when on the job, and is a hunter who shoots a shotgun 15 days each year. Based on the relatively low level of noise exposure, relatively certain protection from the earmuffs, and the fact that gunshots are known to cause hearing loss, a reasonable presumption would probably be that the worker’s hearing loss is not work related. It wouldn’t be a true STS, regardless of the amount of threshold shift observed. The presumption should be that the hearing loss is in fact work related, unless the combination of exposure on and off the job clearly shows that noise exposure at work was unlikely to have contributed to even a portion of the observed hearing loss. While we don’t want to be identifying STSs that are clearly not work related, it certainly won’t hurt to warn the employee of the need for concern, as long as it is made clear that the off-work exposure may likely be the primary cause.

6 STS actions Notify worker in writing within 21 daysRe-train and re-fit hearing protectorsChange to new baseline if STS persistentPossibly record as occupational illness or injuryRefer for medical evaluation if ear infection caused/aggravated by HPDAfter an STS has been identified, taking into account all the considerations previously mentioned, what actions need to be taken by the employer? The first step is written notification of the employee within 21 calendar days. The exact form of this notification is not specified by OSHA, but it should make clear to the employee that an abnormal or excessive amount of hearing loss has been identified, relate this loss to exposure to noise (on and off the job) and emphasize the need for protection from noise. The key point is to provide notification to the worker that his or her health is being harmed, and that action is needed. It may also be necessary, if the worker is currently wearing hearing protectors, to re-train or re-fit as necessary to improve the degree of protection. Of course, if hearing protectors are not being used, then use needs to begin. We’re assuming that the hearing loss would not have occurred if the hearing protection had been adequate. If it is found at this point that the worker can’t successfully use earplugs (which some people can’t), then earmuff use may be necessary.The third action is to change to a new baseline audiogram for future comparisons, if the STS seems to be persistent. The objective is to avoid identifying the same STS every year, which could happen if no baseline change was made. By changing the baseline, only new and additional hearing losses will be identified. The fourth step after identification of STS would possibly be to record the hearing loss as an occupational illness or injury. An STS is not always recordable; a later slide will cover current (2007) OSHA regulations.You may notice that missing from the list of required actions is a mandate to send the worker for medical or audiological evaluation. That is not normally required by OSHA, unless the medical supervisor of the hearing conservation program requires seeing each person identified with an STS. The only time that OSHA requires a medical referral within the hearing conservation program is if there is a medical problem caused or aggravated by the use of hearing protectors. Usually this would be some form of ear infection; if hearing protector use contributed to this condition, then medical referral at the employer’s expense would be required.

7 Baseline revision STS - if present on two consecutiveImprovement - ≥5dB average (2,3,4 kHz) on two consecutive audiogramsGeneral rules:Revise to the better (or earlier) audiogramRevise each ear separatelyRevise all frequencies in each ear togetherSubject to professional judgmentAs mentioned earlier, one of the actions to be taken after determination of an STS is baseline revision. OSHA has never given much guidance on this step, but the National Hearing Conservation Association (NHCA) has stepped in and provided the guidelines listed on this slide. First, revision is only recommended if the STS is determined to be present on two consecutive audiograms, at least six months apart. OSHA also allows baseline revision if there is persistent improvement, defined by the NHCA as 5 dB or greater decrease in thresholds at 2, 3, and 4000 Hz on two consecutive audiograms. The justification for revision in the case of improvement is to provide greater protection for the worker, in that a subsequent STS will be seen earlier if a better audiogram is used for the baseline. If a second audiogram confirms an STS or an improvement, but is slightly different from the first one, the better one of the two should be used, or the earlier one if they are the same. Another recommendation from the NHCA is that each ear be treated separately. A person who has a confirmed STS in the right ear but not in the left ear would therefore have baseline audiograms for the two ears from different years, but all frequencies for each ear would be changed simultaneously. All aspects of baseline revision are subject to the judgment and professional interpretation of the audiometric supervisor, but if something other than this standard procedure is followed, the reasons should be well documented.

8 Recordability of hearing lossMeets all STS requirements andAverage hearing level ≥25 dB at 2, 3 & 4 kHz in the same earRecording requirementsWithin 7 days of test on OSHA 300 logMay later be deleted if change isn’t permanentIn some cases if an STS occurs, it also becomes a recordable occupational illness, according to OSHA regulations. [Of course, some states may have different rules, but the regulations referred to here are federal OSHA requirements.] For the hearing loss to become recordable, it must meet all STS requirements, including work-relatedness, and the average thresholds in the ear where the STS occurred must be greater than or equal to 25 dB at 2, 3, and 4000 Hz. Hearing thresholds beyond the 25 dB range mean that the person is considered to have impaired hearing, and the presence of the STS has either pushed him or her into the impaired category or further into impairment. Once these requirements have been met, the occurrence must be noted on the OSHA 300 Log of injuries and illnesses with seven days of the final determination of the recordable illness. There is now a special column that is marked, as shown on this slide. If further testing, in a future year, shows that this hearing loss was not in fact persistent, then the notation in the Log can be lined out or otherwise deleted.

9 Determination of hearing impairmentAverage thresholds at 0.5, 1, 2, & 3 kHzDetermine degree of impairment, if any0-24 dB, normal range25-39 dB, mild hearing loss40-54 dB, moderate loss55-70 dB, moderately severe loss70-84 dB, severe loss>85 dB, profound lossThe determination of standard threshold shift (STS) requires that an audiogram be compared to an earlier audiogram, the baseline. For determination of hearing impairment or hearing ability, however, we can look at the audiogram in isolation, without doing any comparison with previous measurements. Hearing impairment is normally defined with regard to the speech frequencies: 500, 1000, 2000, and 3000 Hertz. Averaging the person’s thresholds at those four frequencies allows determination of the degree of hearing impairment, if any. We generally define speech frequency average thresholds averaging less than 25 dB as normal hearing, which is not the same as perfect hearing, but instead is hearing ability that allows a person to successfully carry on conversations without significant impediment and otherwise hear what most people hear. If the average threshold is above 25 dB, then some degree of impairment is said to exist, and the degree is specified by the table presented on this slide. Keep in mind that these calculations are done for each ear separately. There is no OSHA requirement to make the impairment calculations – it is just done for additional information for the hearing conservation program and for possible consideration of compensability under a state workers’ compensation system.

10 Percentage of hearing lossAverage thresholds at 0.5, 1, 2, & 3 kHzSubtract 25 dB from result (normal hearing)Multiply result by 1.5%Repeat for each ear500100020003000Avg.%Right Ear20254027.54Left Ear30354532.511In addition to making a qualitative determination of hearing impairment, we can also do a mathematical or quantitative estimation of impairment, expressed as the percentage of hearing loss. This is most often done for workers’ compensation purposes since the amount of compensation for hearing loss is based on a formula such as the one we will consider here. There are a number of different formulas used by various states, but this one is endorsed by the major medical associations. We start by averaging the thresholds in the speech frequencies, 500, 1000, 2000, and 3000 Hertz, just as we did when determining the qualitative hearing loss. The next step is to subtract 25 dB, in order to see how much the average thresholds exceed the normal range. Finally, we multiply that result by 1.5%, a value chosen so that thresholds exceeding 90 dB will be equivalent to about a 100% hearing loss. This process is done separately for each ear to determine the percentage hearing loss. The table on this slide shows an example in which the right ear has an average speech frequency threshold of 27.5 dB, equating to a hearing loss of approximately 4%. The left ear has 5 dB more average loss, so the hearing loss calculates to 11%. We see some degree of impairment in each ear, with the left ear having more loss.

11 Binaural impairment calculationSince hearing isn’t averaged by ears, consider better ear more stronglyMultiply loss in better ear by 5Add loss in poorer earDivide total by 6 for binaural loss(4% x %) = 31%31% ÷ 6 = 5%The previous slide showed a calculation of percentage hearing loss ear by ear. To find the overall impairment, we could simply average those two values, but that wouldn’t necessarily be correct. In actuality, the better ear should be given more weight in the calculation. As an analogy, imagine a person with perfect vision in one eye, but no vision at all in the other. He would have some visual impairment, but surely not 50% since one can function quite well with one eye. The same is true for hearing, so the formula for calculating binaural impairment starts by multiplying the hearing loss in the better ear by a factor of 5 to account for this non-symmetrical disability. After the poorer ear loss is added, the sum is divided by 6 (the sum of 5 and 1) to determine the binaural loss. Using the losses of 4% and 11% from the previous slide therefore calculates to a binaural loss of about 5%. The choice of the number 5 for weighting may seem somewhat arbitrary, but this is the standard procedure for binaural calculation.

12 Problem audiograms - medicalLarge shift in short periodLarge shift in one ear onlyEar pain, dizziness, onset of tinnitusMost of the time, the audiometric technician can give the audiometric test and do basic interpretation of the results with minimal supervision or direct oversight by the professional supervisor. However, sometimes there are problems that need consultation. These problems, as listed on this slide, may indicate potential medical problems beyond simple noise-induced hearing loss. A large shift in a short time, such as an average of 10 dB or more in a year, might be cause for concern, particularly if there is even minimal participation in hearing protection. Even more alarming would be a substantial loss in only one ear, since noise-induced hearing loss is more often somewhat symmetrical. There may be situations where one ear is considerably more exposed than the other,(industrial example here) such as a worker who stands with the source of the noise exposure at one side or the other) but usually a non-symmetrical loss in a short time is cause for concern for a medical cause of the hearing loss.. If the person also reports any ear pain, dizziness, or tinnitus (ringing in the ear), that would be further indication of a potential medical problem that needs referral to a specialist.

13 Problem audiograms - measurementCross hearing situationUncooperative or difficult subjectHearing impaired subjectThere may also be measurement problems that the audiometric technician won’t be able to handle. One of these is known as “cross hearing”, where one ear has much better hearing than the other. This situation has already been discussed under the section about quality control of the audiometric process as an example of a circumstance where an audiologist would need to do the assessment. The same would be true for subjects who are uncooperative or otherwise difficult. Sometimes the subject isn’t trying to be difficult, but may have a coordination problem that interferes with the process of pressing the button at the appropriate time after hearing the tone. It’s not common, but it’s also possible that a person would have so much hearing loss that an accurate assessment using typical industrial instruments would be impossible. These are situations in which the techniques and training of the audiologist are needed

14 Referral to specialistMedical problemsEmployer payment?Measurement problemsInterpretation problemsStandard threshold shift - work related?Recordable on OSHA log - work related?Baseline revisionLet’s then summarize the situations when a referral may be needed. For medical problems, referral may be made to either a specialist or a general physician if any hearing loss cause other than normal, gradual occupational loss is suspected. According to OSHA, the employer is required to pay for this referral only if the problem is one that is caused or aggravated by the use of hearing protectors. Otherwise, the employee is financially liable, although of course in many situations the employer-provided health insurance will cover part or all of the cost. For measurement problems where the technician can’t make reliable and accurate threshold readings, the services of an audiologist would be needed, and the employer would be responsible for the expense. Lastly, there may be interpretation problems, such as questions of work-relatedness and baseline revision where the technician will normally need consultation with the program supervisor or other specialists. This authority may for some simple cases be delegated to the technician, but the professional supervisor still must take responsibility for the decisions.

15 Recordkeeping What audiometric records must be kept How long to keepName of employee & examiner, date of testThreshold resultsCalibration date of audiometerNoise exposure assessment of employeeHow long to keepOSHA: duration of employmentOthers: extended periodOther records to keepBackground noise, hearing history, training of examiner, daily calibration logAn important element of the audiometry program is recordkeeping, with some records required by OSHA and others suggested by good practice standards. The OSHA requirements include such basics as the names of both the employee and the audiometric technician, the calibration date for the instrument, and the employee’s noise exposure. All of this information is needed to help someone at a later date decide if this is a valid audiogram and what is the chance that any hearing loss is caused by on-the-job exposure. OSHA requires that these records be kept for the duration of the worker’s employment, although common sense would suggest keeping the records for at least a few years past the date of separation of the employee, since workers’ compensation claims may be filed after employment ends, depending on specific state law. Considering that the records may be kept in any form, there is really little reason for discarding them. Other records that should be kept despite lack of a specific and formal requirement from OSHA include background noise readings, technician training verification, the employee’s hearing history (which should include off-job exposure and use of protection), and the daily checks on the audiometer. Any records that help to accomplish the goals of verification of audiogram accuracy and actual worker exposure should be maintained for an indefinite period.

16 Summary Interpretation Referral of problem audiograms RecordkeepingSTS calculation - 10 dB 2,3,4 kHzSTS actions and recordabilityImpairment to 3000 Hz, >25 dBReferral of problem audiogramsMedicalMeasurementRecordkeepingIn this part of the lecture we’ve covered basic interpretation of audiograms for occupational health purposes. Remember that there are two common calculations: STS for OSHA purposes and impairment or percentage hearing loss for workers’ compensation uses. The STS calculation compares each ear to the baseline at the most sensitive frequencies, with 10 dB or more of shift requiring action in the form of worker notification, protector refitting and retraining, and in some cases, recording as an occupational illness if the person’s hearing is outside of the “normal” range. The impairment calculation, on the other hand, compares a person’s hearing thresholds to the reference value of 25 dB, the upper limit of “normal” hearing.We also discussed the referral of subjects who have medical abnormalities or who present measurement difficulties to either a physician or an audiologist. The audiometric technician always needs to keep in mind the limitations of his or her training, and when in doubt, refer it out. Lastly we discussed the importance of thorough recordkeeping. The measurements taken by the technician are a very valuable medical/legal record, but lose a portion of their utility if not recorded and maintained in a way that ensures their validity.